Comments are added after the first line that starts with [[AddComment]].

The AddCommentMacro supports previewing and adheres to the TracPermissions scheme, only allowing comments to be added if the user has write access to the page.

Since [21] the AddCommentMacro can fulfill the role of an append only Wiki page. By passing the argument appendonly to the macro, comments can be appended to the page even when the user does not have permission to modify the page. This is potentially unsafe, but can be useful.